Multiple casting apparatus and method

ABSTRACT

An apparatus and method for pressure casting a battery part wherein an extendible piston includes sidewalls for shutting off the supply of molten lead and an impact surface that extends in a side-to-side condition to form an end surface of a battery part cavity so that when the extendible piston is brought into an intensifying condition the extendible piston shuts off further supply of molten metal while a heat source maintains the lead in a molten state as the impact surface of the piston forms a side-to-side mold cavity surface to complete the mold cavity surface thereby eliminating unevenness in the surface of the finished battery part by generating a force with the extendible piston which is sufficient to form a battery part so that upon removal from the mold the batter part is substantially free of tears and cracks as well as surface irregularities.

CROSS REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation of U.S. patent applicationSer. No. 12/470,363, filed May 21, 2009, which is a continuation of U.S.patent application Ser. No. 11/709,365, filed Feb. 22, 2007, which is acontinuation of U.S. patent application Ser. No. 11/058,625, filed Feb.15, 2005, which is a divisional of U.S. patent application Ser. No.10/683,042, filed Oct. 9, 2003, now U.S. Pat. No. 6,866,087, which is adivisional of U.S. patent application Ser. No. 10/112,999, filed Mar.29, 2002, now U.S. Pat. No. 6,701,998. The disclosures of all theabove-listed applications are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

This invention relates generally to pressure casting and, morespecifically to die casting of lead or lead alloy battery parts such asbattery terminals to form a finished battery part while at the same timeinhibiting the formation of cracks and tears during and after thesolidification of the battery part through peripherally contracting themold cavity volume by bringing an entire mold face toward a mold cavityto reduce the bounded surface volume of the mold cavity withoutdisrupting the integrity of the faces of the mold part solidifyingwithin the bounded surface volume.

BACKGROUND

Battery parts such as battery terminals, which are typically made oflead or a lead alloy, are usually cold formed in order to produce abattery terminal that is free of voids and cracks. If lead or lead alloybattery parts are pressure cast, air is left in the battery part cavityin the mold so that as the lead solidifies, the air bubbles prevent thebattery part from cracking. That is, the air bubbles act as fillers sothe lead remains distributed in a relatively uniform manner throughoutthe battery part. Unfortunately, air bubbles within the battery partscause the battery parts to be rejects as the air bubbles can producelarge voids in the battery part. In order to minimize the air bubbles inthe battery part, a vacuum can be drawn in the battery part cavity mold;however, although the vacuum removes air from the mold and inhibits theforming of air bubbles in the battery part, the battery parts cast witha vacuum in the battery part cavity oftentimes solidify in an unevenmanner producing battery parts with cracks or tears which make thebattery parts unacceptable for use.

The process of pressure casting or die casting of battery parts whereinintensification of the battery part is used to form battery partssubstantially free of cracks and tears is more fully described in myco-pending applications U.S. Ser. No. 09/170,247, filed Oct. 13, 1998,titled Apparatus for and Method of Casting Battery parts; U.S. Ser. No.09/458,198 filed Dec. 10, 1999 titled Multiple Casting Apparatus andMethod and U.S. Ser. No. 09/321,776 filed May 27, 1999 titled Apparatusand Method of Forming Battery Parts which are herein incorporated byreference.

In one such embodiment, a battery part is cast which is substantiallyfree of cracks and tears by pressure casting a lead alloy while a vacuumis being applied to the battery part cavity. At the moment when the leadin the battery part cavity reaches the liquid-to-solid transformationstage, the part is intensified by driving a piston into the mold cavityto rapidly reduce the volume of the mold for solidification. Byprecisely controlling the time of application of an external compressionforce to the molten lead in the battery part cavity, and consequently,the time at which the volume of the battery part cavity is reduced, onecan force the molten lead or lead alloy in the flowable state into asmaller volume where the pressure on the battery part cavity ismaintained. By maintaining the pressure on the battery part cavityduring the solidification process by intensification (driving a pistoninto the lead), the battery part can be cast in a form that issubstantially free of cracks and tears.

In another embodiment, the mold for forming the pressure cast batterypart is sealed off while the molten lead is still in the molten stateand before the molten lead can begin to solidify the supply ofpressurized lead is shut off and at the same time the internal pressureof the molten lead is increased by driving a piston into the moltenmetal. This intensification process is suited for those applicationswhere the entire mold can withstand the higher pressures. That is, whenthe liquid metal is in a molten state an increase in pressure of themolten lead throughout the mold and the maintaining of the increasedpressure during solidification can produce a battery part free of tearsand cracks. This process of intensification by driving a piston into themold allows one to obtain greater molding pressure than is availablewith conventional pressure casting techniques.

In another embodiment, the cast battery part is subjected to at least apartial cold forming during the volume contraction step by rapidlydriving a piston into the solidified cast battery part with sufficientforce to cold form a portion of the lead in the battery part to therebyproduce a battery part that is free of cracks and tears. This method ofpartial cold form intensification is more suitable for those batteryparts where one does not want to subject the mold to excessively higherpressures than the die casting pressures.

In the present invention a finished battery is die cast which issubstantially free of cracks and tears is formed by extending a pistonthat first shutoffs the flow of molten lead into and out of the moldcavity. Further extension of the piston brings a piston face that formsa bounded end face of the mold part toward the other faces of the mold.Instead of driving a piston into the mold cavity to increase thepressure of the die cast battery part the entire mold face is broughttoward the set of other mold faces to decrease the volume of the mold.Thus the shutoff and intensification are accomplished by a single strokeof an extendible piston carrying a mold face thereon.

By finished surface it is meant that the surface of the battery does notcontain flashing or irregularities where the molten lead was suppliedthrough a gate. That is, in die casting the runner that supplies lead tothe mold is usually broken off when the battery part is removed from themold thus leaving an unfinished surface. Since irregularities can createproblems in electrical operation of the battery part it is desired tohave a smooth finished surface over the entire battery part. As pointedout, such finished surfaces are usually obtained only with cold forminga battery part. The present invention provides such a finished surfacewithout having to cold form the battery part. In addition, one can alsoincrease the pressure sufficiently to inhibit voids and cracks in thebattery part.

In the present invention a retractable piston has an impact surface ormold face that forms an entire side-to-side mold face or mold surface ofthe battery part thereby eliminating the formation of a localirregularity in the portion of the surface of the battery part thatwould occur if the piston penetrated a portion a mold face i.e. breakingthe surface plane of the mold cavity. The use of a side-to-side orbounded mold face that does not break the surface plane of the moldcavity substantially eliminates the need to finish the battery part.That is, once the part is removed from the mold it is ready for usesince the surface plane of the mold cavity has not been broken orpenetrated by the moving end face. In addition, since the entireside-to-side surface of the battery part is impacted the precisiontiming of the intensification step is eliminated. That is, since theintensification pressure is applied on a side-to-side portion of thebattery part cavity the lead can be in either the liquid, solid or mushstate since the all the lead can be confined and squeezed within thecavity of the battery part mold cavity.

SUMMARY

An apparatus for pressure casting a battery part wherein a mold includesa set of faces to form a portion of a battery part mold cavity and anextendible piston having a battery part mold cavity face that extends ina side-to-side condition on the piston with the faces coacting to form abounded battery part mold cavity. The piston includes sidewalls forshutting off the supply of molten lead to and from the mold cavity sothat when the extendible piston is brought toward the battery part moldcavity the extendible piston first shuts off a further supply of moltenmetal to the battery part mold cavity as well as egress of metal fromthe battery part mold cavity to create a closed battery part moldcavity. The battery part mold cavity peripherally contracts as the faceof the piston forms an entire bounded face of the battery part moldcavity. The peripherally contraction eliminates localized surfacepenetration of the face of a battery part as the peripheral surface ofthe cavity remains intact as it is decreased. The result is the batterypart in the battery part mold cavity have non-disturbed faces when thebattery part mold cavity is brought to a closed condition. Ifintensification is desired one maintains the pressure on the lead as itsolidifies so that upon solidification the part is substantially free oftears and cracks as well as surface irregularities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of the apparatus of the mold andextendible pistons for forming a battery part in an open condition;

FIG. 2 is partial sectional view of the apparatus of FIG. 1 showing oneof the extendible pistons extended to form part of an interior surfacefor a battery part and the other extendible piston in a retractedcondition to allow molten lead to flow into the mold;

FIG. 3 is the partial sectional view of the apparatus of FIG. 1 showingthe extendible piston in an engaged condition that prevents furthermolten lead to from flowing into the battery part cavity and at the sametime intensifying the lead in the battery part cavity;

FIG. 4 shows an isolated view of the multiple mold surfaces that coactto form a battery part mold cavity wherein moving an end face of themold cavity contracts the volume of the cavity;

FIG. 5 shows an isolated view of the mold faces with the mold cavity inan open condition to allow flow of molten lead therein;

FIG. 6 is an isolated view of the mold faces of FIG. 5 with the end facein a sealing condition or closed mold condition; and

FIG. 7 is an isolated view of the mold faces of FIG. 5 with the moldcavity in a contracted condition.

DETAILED DESCRIPTION

FIG. 1 is a partial sectional view of apparatus 10 for faceintensification during die casting of battery parts. Apparatus 10includes an upper first mold part 11 and a lower second mold part 12that are held proximate each other by a member (not shown) to form acavity 16 therein. The two parts are joined a parting surface 12 p thatextends between the two mold parts.

Located partially in mold part 11 is a first extendible cylindricalpiston 14 which is axially slideable into mold part 11. Piston 14includes a cylindrical surface 14 a for slideingly engaging cylindricalsurface 11 a in mold part 11 to prevent molten lead from flowingtherepast. The end of piston 14 includes a hemispherical recess 14 c andan annular impact surface 12 e there around with the annular impactsurface 12 e located in a single plane. Extendible piston 14 slidinglyengages the sidewall 11 a of mold part 11 to allow for axial insertionthereof to bring the impact surface 12 e downward to become a portion ofthe battery part cavity surfaces formed by the sidewalls of cavity 16.That is, the impact surface 12 e forms an entire end or side-to-side topsurface to the battery part cavity 16 thereby preventing formation oflocal irregularities in the end surface of a battery part cast since theentire end face 12 e can be brought inward to form the battery part moldcavity.

Extending downward into mold part 11 is a first runner or gate 17terminating in a mouth 17 a and a second runner 18 or vent terminatingin a mouth 18 a. Runner 17 is connected to a supply of molten lead (notshown) and vent 18 connects to a vent valve 18 to allow air to escapefrom the mold cavity. Located around the mold part 11 is a heater 20 formaintaining the temperature of the upper portion of mold part 11sufficiently hot to maintain the lead in runners 17 and 18 in a moltenstate during the intensification and casting of a battery part.

Located beneath mold part 12 is a cylindrical pin 13 for that extendsthrough cavity 16 and into a cylindrical sleeve 15 in piston 14. Pin 13has a cylindrical surface 13 that slidingly engages cylindrical sleeve15 to maintain a sliding relationship between piston 14 and pin 13.

FIG. 2 is partial sectional view of the apparatus of FIG. 1 showing thepin 13 extended upward into battery part cavity 16 to form part of aninterior surface for a battery part. The top extendible piston 14 is ina retracted condition to allow molten lead to flow into the mold cavity16 through the runners 17 and excess lead and air to evacuate throughrunner 18, as indicated by the arrows. Thus as evident by FIG. 2 themolten lead flows around the extendible piston 13 into the annularbattery part cavity 16. Note, at this point end annular surface 12 eforms no part of the contiguous boundary wall of the battery part cavity16. That is the mold cavity is in an open condition so that molten leadcan flow into cavity 16 thought gate 17.

While the present battery part cavity is shown with an annular shapedbattery part cavity one can use the present process without a pin 13 toobtain a non-annular shaped battery part.

FIG. 3 is the partial sectional view of the apparatus of FIG. 1 showingthe extendible piston 14 in an engaged or closed condition that preventsfurther molten lead from flowing into or out of the battery part cavity16 and at the same time in a condition that one can intensifies the leadin the battery part cavity 16 to inhibit the formation of tears andcracks. In the position shown, the sidewalk 14 a of piston 14 close offthe mouths 17 a and 18 a to prevent further molten lead from flowinginto or out of battery part cavity 16. Molten lead 30 is shown inbattery part cavity 16 as well as in runners 17 and 18.

During the extension of member 14 excess molten lead in chamber 31 isforced backward or backwashed into runners 17 and 18 until the end ofextendible piston covers the mouths 17 a and 18 a of the runners 17 and18. This ensures that the mold cavity is filled with molten lead. Atthis point battery part cavity 16 becomes closed as no lead can leavethe battery part cavity. Further downward pressure on extendible piston14 brings end face 12 e downward decreasing the volume of the batterypart cavity without penetration of a surface. By maintaining thepressure one intensifies the cast part by increasing the internalpressure of the lead in the battery part cavity 16 sufficiently high sothat when the lead solidifies the part is substantially free of tearsand cracks. Thus, the intensification process of the present methodcomprises creating an abrupt increase in the internal pressure of thelead in a mold cavity to a level which is sufficient to reduce the sizeof trapped air bubbles therein by bringing an entire face of the batterypart mold cavity toward the other mold faces so that when the batterypart solidifies the battery part is substantially free of cracks andtears.

In the embodiment shown the annular end 12 e of the extendible piston 14is driven to an adjoining condition at the corner line of the cavity ofthe battery part cavity surface 16 in mold part 11. By having the impactsurface 12 e form the entire bounded top surface of the battery partcavity one eliminates the formation of irregularities in the finishedbattery parts since the top surface of the battery part cavity remains acontinuous surface.

FIG. 3 shows that the battery part cavity is formed of multiple surfacesor faces some of which are formed by the extendible piston and othersthat are formed by the mold parts. That is, the battery part cavity hasan interior surface 12 d formed by piston 13. Mold part 12 includesannular mold part surface 12 b and lateral mold part surface 12 a. Moldpart 11 includes the lateral mold part surface 12 c with impact surface12 e defining the final surface portion of the battery part.

As can be seen pin 13 slidingly mates with the cylindrical recess 14 cin piston 14 thus ensuring that both pin 13 and piston 14 are in axialalignment and that the interior surface of the cast part is centrallypositioned within the battery cavity 16.

With the present apparatus and method one eliminates any runner marks aswell as intensification marks on the finished battery part since thebattery part is contiguously defined by the coactions of the extendiblepistons and the battery part molds. In addition, the alignment of theextendible pistons allows for an on-the-go formation of the batterycavity.

In the present process the method of die casting a finished battery partwhile minimize cracks and voids in the battery part includes the stepsof forming a mold 11, 12 with the mold defining a plurality of faces 12a, 12 b, 12 c 12 f for a first portion of a battery part mold cavity 16.One forming a gate passage 17 that fluidly connected to the firstportion of the battery part mold cavity 16 when the mold is in a pouringcondition. One forms a moveable member or piston 14 the moveable memberincludes a portion 12 e defining a further face of the battery part moldcavity 16 with the plurality of faces 12 a, 12 b, 12 c 12 f and thefurther face 12 e defined a surface bounded mold cavity when themoveable member is in a closed condition as illustrated in FIG. 3. Bypouring a lead containing metal in a fluid state into the gate 17 of themold when the mold cavity 16 is in an open condition as illustrated inFIG. 2 allows molten lead to flow into the mold cavity 16. By allowingthe lead containing metal to fill the first portion of the battery partmold cavity 16 of volume V1 (FIG. 4); and then driving the moveablemember 14 toward the first portion the battery mold part one closes offthe gate passageway 17 and the vent passage 18. One continues to drivethe movable member 14 toward the first portion of the battery mold partcavity 16 until the further face 12 e forms the final surface to closethe mold cavity 16. By applying pressure to member 14 one can increasethe internal pressure of the lead in the mold increases sufficiently toforce lead into any solidification voids formed in the batter part.Next, one allows the battery part to solidify under pressure. Once thebattery part is solidify one can removing the mold from the battery partto produce a finished battery part.

The method of forming a finished battery part can be obtained by pouringa lead containing metal in a liquid state into an open battery cavity 16defined by a first set of faces in a battery part mold and allowing thelead containing metal to solidify around the first set of faces in thebattery part mold and then driving a member having a portion defining acompletion face 12 e toward open battery cavity 16 until the completionface 12 e and the first set of faces coact to form a closed surface forthe battery cavity. By maintaining pressure on the batter part thereinduring solidification of the metal in a liquid state it forces moltenlead to flow into any solidification voids formed during solidificationphase of the molten lead in the battery part cavity.

FIG. 4 illustrates the set of faces for forming the die cast batterypart. For ease in comprehension the mold parts have been left out withexception of the faces that form the mold cavity. That is the set ofmold faces comprises a cylindrical interior face 12 c, a lower end face12 b, a lower side face 12 a, an upper side face 12 c, a cylindrical endface 12 f and a top end face 12 e. These set of faces form the boundarysurfaces for defining the battery part which is die cast with thepresent invention. The surfaces defined by the set of faces have avolume designated by V₁. It is within the volume V₁ that the finishedbattery part would solidify into a battery part with minimum cracks andtears.

In order to illustrate the volume of the battery part mold cavity V₂ inthe unreduced state dashed lines have been included to illustrate theposition of the gate 17 for supplying molten lead to the cavity as wellas the vent 18 for discharging air and excess lead. The annular surfaceidentified as 12 e identifies the position of the mold when the mold isin an open condition and the annular surface 12 e identified theboundary of the mold cavity 16 in closed condition but not yet in apressurized condition. V identifies the contracted volume₁. Thus the endannular face 12 e can be brought downward to decrease the first volumeV₂ of the battery part cavity by forcing the annular mold face 12 etoward the battery part cavity 16 while the molten lead in the batterypart cavity is at least partially in an unsolidified state. Bymaintaining the battery part cavity 16 in a decreased volume during asolidification of a battery part one inhibits the formation of cracksand tears in a die cast battery part.

Thus the method of die casting a battery part comprises injecting a leadcontaining metal in a molten state into an open battery part cavity 16which is partially defined by a mold 11 and 12. By closing the batterypart cavity 16 by bringing a member 14 with a finished mold face 12 etoward the open battery part cavity 16 partially defined by the mold 11and 12 one shuts of the passage ways 17 and 18 to create a closedbattery part cavity 16 to thereby prevent further lead containing metalin a molten state from entering or leaving the closed battery partcavity 16. By increasing the pressure of the lead in the closed batterypart cavity 16 one can force lead that is in a molten state in thebattery part cavity into any solidification voids in lead in the closedbattery part cavity 16 to thereby inhibit the formation tears and cracksin the batter part.

The present method can include the step of maintaining the mold faces ata temperature below the solidification temperature of the molten lead tocause peripheral surface solidification. By allowing peripheral surfacesolidification to occur before the volume contraction occurs one canforce the molten lead into voids and cracks in the peripheral surfacesolidification thereby inhibiting the formation of solidification voidsin the die cast part.

Thus with the present process one can form an unfinished die castbattery part with the die cast battery part having a set of boundedfaces with each of said set of bounded faces adjoining each other todefining a closed surface for the battery part. Each of faces 12 a, 12b, 12 c, 12 f and 12 e are characterized by having a continuous boundedsurface free of surface imperfections so that a battery part formedwithin the cavity is also free of surface imperfection when the die castbattery part is removed from a die cast mold.

FIG. 5, FIG. 6 and FIG. 7 illustrate the various conditions of thecavity during the process of solidification.

FIG. 5 shows the mold in the open condition with the set of mold faces12 a, 12 b, 12 c 12 d and 12 f forming the lower battery part moldcavity. This state is referred to as an open mold cavity since moltenlead can enter the mold cavity through the open annular top of moldcavity 16. In this condition the mold part cavity 16 can be filled withmolten metal.

FIG. 6 shows the mold in the closed condition with the set of mold faces12 a, 12 b, 12 c 12 d and 12 f forming the lower battery part moldcavity and annular face 12 e forming the top face of mold cavity 16.This state is referred to as a closed mold cavity since molten leadcannot enter or leave the mold cavity 16. In this condition the moldpart cavity 16 forms a bounded or confined region for the molten metal.Note in this condition the downward movement of piston 14 has sealed offboth the inlet and outlet to the mold cavity 16. Extending laterallyoutward is a cavity closing line SL that identifies the point whereinthe sidewalls of piston 14 close off both the inlet and outlet for metalto the cavity 16.

FIG. 7 shows the next phase wherein piston 14 has been extended beyondthe cavity closing line S_(L) a distance x. Note, the entire face 12 ehas been moved toward the mold cavity 16 to decrease the volume of themold cavity 16. This is the contracted condition wherein the pressure ofthe molten lead has been increased sufficiently so that it inhibits theformation of tears and cracks in the solidified metal. FIG. 7illustrates that the entire face 12 e moves downward along sidewall 12 fto not only reduce the volume of cavity 16 but to reduce the peripheralsurface area of the faces forming the cavity 16. In addition, since theentire face 12 e moves toward the cavity 16 to contract the volume ofthe cavity the solidifying battery part surfaces are not disturbed. Thisresults in a die cast product that, when removed from the mold, has afinished surface condition, thus eliminating the need for an extra stepof finishing the product.

1. An apparatus for die cast battery part when the molten lead is ineither the liquid, solid or mush state to form a finished battery part:a mold having a set of faces for defining a portion of an outer surfaceof a battery part cavity; a pin having a face thereon, said pinextending through the battery part cavity to form an inner face of abattery part cavity; an inlet for delivering lead in a molten state intothe battery part cavity; a heater for maintaining the lead in a moltenstate when the lead in a molten state is not being delivered into thebattery part cavity; a retractable piston, said retractable pistonhaving a battery part face thereon for forming the battery part cavityinto a closed volume, said battery part face extending in a side-to-sidecondition to adjoin the set of faces in the battery part cavity, saidretractable piston positionable in a first condition to allow the leadin a molten state to flow into the battery part cavity, said retractablepiston driveable toward the battery part cavity to close the volume ofthe battery part cavity to thereby shut off the flow of the lead in amolten state into the battery part cavity and to decrease the closedvolume of the battery part cavity by bringing the battery part facetoward the battery part cavity to shrink the volume of the battery partcavity without disrupting a faces on a solidifying battery partsolidifying therein to produce the battery part with an exteriorfinished surface.
 2. The apparatus of claim 1 wherein the retractablepiston has a cavity for sliding along a pin and the pressure of the leadwithin the battery part cavity is increased sufficiently to thereby forma battery part whereupon solidification is substantially free of tearsand cracks.
 3. The apparatus of claim 1 wherein the battery part facecomprises an annular face.
 4. The apparatus of claim 3 wherein theentire battery part face extends along a single plane.
 5. The apparatusof claim 1 wherein the lead in a molten state is a lead alloy.
 6. Theapparatus of claim 1 the heater extends around the inlet to maintain thelead in the inlet in a molten state when the extendible piston is in anextended condition.
 7. The method of die casting a finished battery partwhile inhibiting the formation of cracks and tears comprising the stepsof: directing a first charge of lead in a molten state into a batterypart cavity having at least one open face; extending a retractablepiston having a battery part face into the charge of molten lead in thebattery part cavity to shut off the supply of molten lead to the batterypart cavity; and continuing to extend the piston to form a closedbattery part cavity and to reduce the volume of lead in the battery partcavity to a sufficient volume so that upon solidification of the lead inthe battery part cavity it inhibits the formation of cracks and tears inthe battery part.
 8. The method of claim 7 wherein the lead in thebattery part cavity is in either a liquid, mush or solid state.
 9. Themethod of claim 8 wherein the molten lead solidifies along the surfacefaces of the battery part cavity with at least one of the battery partfaces is forced inward to reduce the volume of the battery part cavity.10. The method of claim 9 including the step of heating the first moldpart with a heater to maintain the mold in a runner in a molten state.11. The method of claim 7 wherein a portion of the lead in a runner isback flowed therein to bring the molten lead in the battery part cavityto an intensification condition.
 12. The method of die casting afinished battery part comprising the steps of: injecting a molten leadcontaining metal into a battery part cavity having a first volumedefined by a set of mold faces; and decreasing the first volume of thebattery part cavity by forcing at least one of the mold faces toward thebattery part cavity to decrease the peripheral surface area while themolten lead in the battery part cavity is at least partially in anunsolidified state; and maintaining the decreased volume during asolidification of a battery part in the battery part cavity to therebyinhibit the formation of cracks and tears in a die cast battery part.13. The method of claim 12 wherein the battery part cavity is formedwith a cylindrical interior surface and an annular end face. 14-25.(canceled)